The invention relates to lightweight heat radiating apparatus that is useful in spacecraft for ejecting heat energy from such craft into space. More particularly, the invention relates to a liquid droplet radiator that contains magnetic means for focusing a sheet of liquid droplets as it flows between a droplet generator and a collector, thereby to improve the efficiency with which the collector operates, while maintaining the overall weight of the collector desirably low.
One of the more pressing thermal management problems confronting designers of large, complex and more powerful spacecraft of the future is the need to reject energy from the spacecraft's power cycles without ejecting mass into space. Typical heat energy generating power cycles in spacecraft include the refrigerators that are needed to keep cryogens in a liquid state (as well as to cool charged particle accelerators), high powered radar, large IR detector arrays, in addition to a wide range of other on-board cooling applications. The only means available for rejecting energy from a spacecraft without exhausting mass into space is to radiate the energy from the spacecraft into the colder ambient surrounding the craft.
It is desirable from a thermodynamic viewpoint to reject energy from a spacecraft at relatively low temperatures, therefore, very large radiating areas are ordinarily required. In many of the power cycles utilized on spacecraft, the peak temperatures are often fixed by materials limitations, thus, an increase in the energy rejection temperature can have an adverse impact upon the efficiency of the power cycle. Because of such considerations, the energy rejecting radiators historically utilized in spacecraft have comprised a massive part of their power system. In alternative system designs, spacecraft power systems have been designed to operate between fairly small temperature differences in order to reduce the size of radiators needed, however, that expedient results in the need to make all other components relatively large and unwieldy.
In the past, many different types of energy radiating devices have been designed in an attempt to overcome this dilemma between the need for a large energy radiating surface and the need to minimize the overall weight of an energy radiating system. Some of the concepts that have been pursued relatively recently as energy radiating mechanisms for use in spacecraft are radiator designs that utilize dust, moving belts, thin radiating tubes, heat pipes, and energy radiating droplets. All of those concepts have shown some promise for being maturable into acceptably lightweight energy radiating systems for application in spacecraft; however, an optimum energy radiating system for spacecraft is still needed. As spacecraft payloads continue to increase in size, this need will be heightened, due to the resultant increase in the more complex, more powerful and heavier management systems that will be added to such future craft.
The magnetically focused liquid droplet radiator of the present invention is believed to be a major advance over all known prior art systems that have been proposed for spacecraft application. One of the basic design constraints that must be dealt with in order to enable a liquid droplet radiator system to be applied in a spacecraft energy radiator is that the collector unit for such a system needs to have a very high efficiency. Losses of liquid coolant from the system must be limited to fractions of ppm (parts per million) in order to minimize both spacecraft contamination, and the need to minimize weight penalty resulting from having to provide makeup liquid coolant to the system. In a spacecraft application, losses of energy radiating coolant fluid can result from a wide range of events or conditions such as the following:
1. Directional dispersions of the liquid droplets as they leave the droplet generator.
2. Velocity dispersions of the droplets as they leave the droplet generator.
3. Electrical charge accumulations on the liquid droplets, which result in dispersions of the droplets due to Coulombic repulsion.
4. Evaporation of the liquid coolant.
5. Spacecraft accelerations.
6. Incident post radiation, which is capable of imparting random forces to the liquid droplets.
7. Splashing of the liquid droplets in the droplet collector of the system.
8. Random collisions between droplets distributed from the droplet generator.
Such losses of energy radiating fluid can be at least partly overcome with two different design approaches. First, a larger liquid droplet collector can be utilized in the radiator system to provide a bigger target within which randomly dispersed droplets can be collected. That approach has major disadvantages in terms of greater weight penalty, larger radar cross section, and other unattractive characteristics. Moreover, a larger collector does not guarantee that splashing would not continue to pose a potential loss mechanism. A second, more desirable approach is to provide a force field, which can be either electric or magnetic, and which can be applied to the liquid droplet particles in order to steer or focus them into a relatively small, light weight liquid droplet collector. The present invention utilizes a magnetic force field to achieve such focusing of a sheet of energy radiating droplets in a liquid droplet radiator system that is designed for spacecraft applications. In order to avoid inherent problems caused by; electrical charges present in a spacecraft, electric charge exchange within a liquid drop radiator, forces within a distributed sheet of energy radiating droplets which tend to blow it up, as well as other considerations, it is thought that the use of a magnetic flux field to focus the energy radiating sheet of a liquid drop radiator is more suitable for spacecraft application than use of an electric focusing field might be.